Magnetic Random Access Memory (MRAM) is an emerging technology that can provide an alternative to traditional data storage technologies. MRAM has desirable properties including fast access times like DRAM and non-volatile data retention like hard disc drives. MRAM stores a bit of data (i.e. information) as an alterable orientation of magnetization in a patterned thin film magnetic element that is referred to as a data layer, a sense layer, a storage layer, or a data film. The data layer is designed so that it has two stable and distinct magnetic states that define a binary one (“1”) and a binary zero (“0”). Although the bit of data is stored in the data layer, many layers of carefully controlled magnetic and dielectric thin film materials are required to form a complete magnetic memory element. One prominent form of magnetic memory element is a spin tunneling device. The physics of spin tunneling is complex and good literature exists on the subject of spin tunneling.
In FIG. 1a, a prior magnetic tunnel junction device 201 includes a data layer 202 and a reference layer 204 that are separated by a thin tunnel barrier layer 206. Typically the tunnel barrier layer 206 has a thickness that is less than about 2.0 nm, for example. In a tunneling magnetoresistance (TMR) structure the tunnel barrier layer 206 is an electrically non-conductive dielectric material such as aluminum oxide (Al2O3), for example. Whereas, in a giant magnetoresistance (GMR) structure the tunnel barrier layer 206 is a thin layer of an electrically conductive material such as copper (Cu), for example.
The reference layer 204 has a pinned orientation of magnetization 208, that is, the pinned orientation of magnetization 208 is fixed in a predetermined direction and does not rotate in response to an external magnetic field. In contrast the data layer 202 has an alterable orientation of magnetization 203 that can rotate between two orientations in response to an external magnetic field.
In FIG. 1b, when the pinned orientation of magnetization 208 and the alterable orientation of magnetization 203 point in the same direction (i.e. they are parallel to each other) the data layer 202 stores a binary one (“1”). On the other hand, when the pinned orientation of magnetization 208 and the alterable orientation of magnetization 203 point in opposite directions (i.e. they are anti-parallel to each other) the data layer 202 stores a binary zero (“0”).
In FIG. 1c, the prior magnetic tunnel junction device 201 is typically positioned at an intersection of two orthogonal conductors 205 and 207. The conductors (205, 207) are also referred to as electrodes, write lines, row conductors, column conductors, word lines, and bit lines. For instance, the conductor 205 can be a word line and the conductor 207 can be a bit line. A bit of data is written to the prior magnetic tunnel junction device 201 by generating two magnetic fields hX and hY that are in turn generated by currents iY and iX flowing in the conductors 207 and 205 respectively. For purposes of illustration, the current iX is depicted as flowing in a direction parallel to a x-axis X and the current iY is depicted as flowing in a direction parallel to a y-axis Y.
The magnetic fields hX and hY cooperatively interact with the data layer 202 to rotate the alterable orientation of magnetization 203 from a current orientation to a new orientation. Therefore, if the current orientation is parallel (i.e. positive x-direction on the x-axis) with the pinned orientation of magnetization 208 such that a binary “1” is stored in the data layer 202, then the magnetic fields hX and hY will rotate the alterable orientation of magnetization 203 to an anti-parallel orientation (i.e. negative x-direction on the x-axis) such that a binary “0” is stored in the data layer 202.
In FIG. 2, the prior magnetic tunnel junction device 201 can be positioned in an array 301 of similar prior magnetic tunnel junction devices 201 that are also positioned at an intersection of a plurality of conductors (207, 205) that are arranged in rows and columns. The configuration depicted is typical of prior MRAM devices. For purposes of illustration, in FIG. 2, the conductors 207 are bit lines and the conductors 205 are word lines. The conductors (205, 207) need not be in direct contact with the prior magnetic tunnel junction devices 201. Typically, one or more layers of material separate the conductors (205, 207) from the data layer 202 and the reference layer 204.
A bit of data is written to a selected one of the prior magnetic tunnel junction devices 201 that is positioned at an intersection of a word and bit line by passing the aforementioned currents iY and iX through the word and bit lines. During a normal write operation the selected magnetic tunnel junction device 201 will be written to only if the combined magnetic fields hX and hY are of a sufficient magnitude to switch (i.e. rotate) the alterable orientation of magnetization 203 of the prior magnetic tunnel junction device 201.
One disadvantage of the prior magnetic tunnel junction device 201 is that a coercivity HC of a material of the data layer 202 is relatively high at a typical operating temperature of the prior magnetic tunnel junction device 201. In FIG. 3, a curve 300 depicts a magnitude of a switching field (i.e. hX and hY) required to rotate the alterable orientation of magnetization 203 as a function of a temperature T mp (on an x-axis) of the data layer 202 and a coercivity HC (on a y-axis) of the data layer 202. The lower the temperature T mp the higher the coercivity HC. Accordingly, at a typical operating temperature of T1, the data layer 202 has a coercivity HC at T1 that results in a switching field SH that is relatively high on the curve 300.
Disadvantages to the high switching field SH include high currents for iY and iX in order to generate the required magnitude of the switching field SH and those high currents require large driver circuits to supply the current. Large driver circuits increase an areal density of the MRAM and generate waste heat. Moreover, a major disadvantage to the high switching field SH is that a magnitude of the fields hX and hY that comprise the switching field SH are such that non-selected magnetic tunnel junction devices 201 in the array 301 of FIG. 2 can have their respective alterable orientation of magnetization 203 switched by the fields hX and hY during a write operation to a selected magnetic tunnel junction device 201. As a result, data stored in the array 301 can be corrupted. The effect of the fields hX and hY on non-selected magnetic tunnel junction devices 201 is referred to as a half-select margin. Ideally, only the data in the selected magnetic tunnel junction device 201 is written to during a write operation.
Consequently, there exists a need for a magnetic tunnel junction device in which a temperature of a data layer is increased during a write operation to the magnetic tunnel junction device so that a coercivity of the data layer is reduced and a magnitude of a switching field necessary to write data to the data layer is also reduced.